Tracing and Healing Multiscale Defects for Cost‐Effective Lithium Carbonate‐Derived Layered Oxide Cathodes

ABSTRACT Lithium carbonate (LC) is markedly cheaper than lithium hydroxide (LH) but remains underused for layered oxide cathodes because LC‐derived materials perform poorly. Here, using a mid‐Ni cathode, LiNi 0.65 Co 0.05 Mn 0.30 O 2 (N65), we trace this performance gap to LC‐induced defects that span length scales, from atomic‐scale disorder to nanoscale and microscale porosity. These defects originate from three features of the carbonate pathway that act across the solid, liquid, and gas phases, namely decoupled dehydration and lithiation, late melting of the carbonate, and a locally oxygen‐deficient atmosphere from evolving CO 2 . Guided by this picture, we heal the defects with a single secondary heat treatment (SH) that adds an optimized amount of LH, simultaneously replenishing lithium, restoring an oxidizing atmosphere, and densifying the structure. The resulting N65‐LC SH achieves discharge capacity, rate capability, and cycling stability comparable to those of the LH counterpart, while cutting the lithium precursor cost by 9% to 16% relative to conventional all‐LH synthesis. More broadly, the gap between LH and LC is not an intrinsic property of the carbonate but a consequence of a precursor‐specific pathway that, once traced, can be engineered around to unlock low‐cost, high‐performance Ni‐based layered oxide cathodes.